1. Field of the Invention
The present invention is directed to a method and apparatus for improving power control in electrical/electronic devices, and more particularly, a method and apparatus for controlling power sequencing for a plurality of electrical/electronic devices such as media drives.
2. Background of the Invention
As electrical/electronic devices become more ubiquitous in today's society, power usage by such devices is becoming a key issue. For any given device, power usage is proportional to heat dissipation and it is thus desirable to reduce power requirements of a device in order to reduce the resultant heat and its associated problems with dissipation of such heat using heat sinks and the like. In addition, the shear number of electrical/electronic devices creates demand on the utility industry to build power plants that provide enough energy to meet peak demands for electrical energy. In similar fashion, when designing power supplies for electrical/electronic systems having many types of components, the power supply for such a system must be designed to meet the maximum, or peak, demand that it will ‘see’ during system operation. Generally speaking, as peak demands get higher, a power subsystem having a higher electrical energy output capability is required to meet such demand, thereby increasing size and cost of such power subsystem.
One type of electrical/electronic subsystem having a plurality of components is a disk array, having a plurality of disk drives, and used to provide data storage to a computer system. A RAID disk array is one such array, having a plurality of physical disk drives logically configured together to present a redundant storage subsystem to a computer. A newer type of disk array now coming to market is known as an ATA disk array, which is composed of a plurality of ATA disk drives. In the past, ATA disks have only been used in lower end computers such as personal computers and lacked the performance and reliability needed at the data center level. But advancements in quality and speeds have more recently made them appealing to vendors seeking a lower price point. A plurality of these relatively low performance drives are now being packaged together to create an ATA disk array having a relatively high performance, and to provide RAID storage subsystems.
In general, disk drives draw a proportionately large amount of current during start-up, as the individual disk platters must be brought from a quiescent power-down state to a run time state where the disk(s) are spinning at their nominal spin rate. Servo motors are typically used to spin the disk drives, and it is these motors that draw the current required to transform the disk(s) from a non-spinning state to a spinning state. The inertia required to go from a non-spinning state to a spinning state is what causes the high surge current or rush-in current at start-up. Once spinning, not as much current is required to maintain a disk in a spinning state. When a large number of disk drives are simultaneously going through their power up sequences and turning-on the motors to spin up the disks, the overall current required to meet this turn-on surge current is the sum of the surge currents of each individual drive.
Certain designs stagger the time when individual disk drives spin-up to thereby provide a smoothing in the overall peak power requirements of the power supply used to power the media drives. However, these types of systems typically use a worst case drive and its associated worst case characteristics when determining the staggered times for spinning up the drives. This can needlessly delay the time from when a system is first powered up to when the all the drives in the system are ready. Excessive delays before the drives are all ready slow system availability at start-up, and in some instances can actually cause certain operating systems to fail their boot-up sequence or otherwise generate system errors because of the excessive delay.
It is thus a problem with disk array systems that either large and expensive power supplies are required to meet this start-up surge current requirement, or excessive start-up delays are introduced when bringing a disk array on-line during power-up. There is a need to develop a method and apparatus that mitigates this high surge current requirement. The present invention is designed to overcome the aforementioned problems.